A) Field of the Invention
This invention relates to a data transmission apparatus and more in detail, is related to a data transmission apparatus to be connected to communication network being capable of isochronous transmission such as an IEEE 1394 network, etc.
B) Description of the Related Art
The IEEE 1394 is well known for a standard of a serial bus interface. In the communication network based on the IEEE 1394 Standards (hereinafter, called the IEEE 1394 network), Maximum sixty-three apparatuses (hereinafter, called the IEEE 1394 device) can be connected to one bus (a local bus).
Generally, by controlling a parameter relating to a bus configuration, a controller that optimizes usage efficiency of the local bus and other nodes are connected to one bus. As the other nodes, for example, there are a talker (a transmission node) and a listener (a reception node). The talker transmits a fixed amount of data (for example, audio stream for 8 channels and MIDI stream for 1 cable) determined in advance of an audio device such as an electronic musical instrument that can output an audio (voice) signal and a MIDI device that outputs a MIDI signal to the bus by one isochronous stream (one isochronous packet transmission in every isochronous cycle). For example, refer to “consumer audio/video equipment—Digital interface—Part 6: Audio and music data transmission protocol”, International Electro technical Commission, Jul. 12, 2002.
FIG. 9 is a schematic view representing a technique for establishing a connection between the transmission plug and the reception plug in the conventional IEEE 1394 devices.
In the talker that is a transmission node, 8 transmission plugs [0-7] are set, and 8 transmission FIFO are set to be agreed with the number of the transmission plugs. Paths between the transmission FIFO [0-7] and the corresponding transmission plugs [0-7] are fixed and cannot be changed.
As same as the transmission node, in the listener that is a reception node, 8 reception plugs [0-7] are set, and 8 reception FIFOs are set in correspondence with the number of the reception plugs. Paths between the reception FIFOs [0-7] corresponding to the reception plugs [0-7] are fixed and cannot be changed.
In the conventional IEEE 1394 device, the number of sequences of the data stream transmitted from the transmission node is fixed, and number of the sequences cannot be increased or decreased dynamically. In an example shown in FIG. 9, when the number of the sequences transmitted from the transmission node is 8, i.e., the sequences Seq [0-7], it is necessary to reserve bandwidth corresponding to the 8 sequences on the IEEE 1394.
For example, as shown in FIG. 9, when a connection is established between the transmission plugs [4] and [5] and the reception plugs [0] and [1], the number of the sequences cannot be increased or decreased dynamically. Therefore, the transmission node needs to transmit all the 8 sequences.
That is, in the conventional IEEE 1394 device, by continuously transmitting data stream without a receiver, the bandwidth is wastefully occupied. For example, when there are the receivers only in channel 7 and channel 8 of the audio 8 channels that are transmitted from the transmitter, channel 1 to channel 6 without receivers spends a wasteful bandwidth. Moreover, in a network equipped with the isochronous transmission function other then the IEEE 1394 network, the number of the sequences transmitted by isochronous transmission cannot be changed dynamically as same as in the IEEE 1394 network.